Knee injuries increasing among young athletes

Sometimes physicians will notice a medical trend well before science confirms its existence. That has been the case with injuries to the anterior cruciate ligament, the main ligament that stabilizes the knee joint, in young athletes. “Doctors who treat kids have all been saying over and over that the numbers of A.C.L. tears are going up dramatically,” says Dr. J. Todd Lawrence, an orthopedic surgeon and pediatric sports medicine specialist at the Children’s Hospital of Philadelphia. But surprisingly little firm data has confirmed that hunch.

So, for a study presented this month at the annual conference of the American Academy of Pediatrics in Boston, Dr. Lawrence and his colleagues parsed emergency room records of pre-adolescent youngsters treated at Children’s Hospital, looking for A.C.L. tears, as well as tears of the meniscus, the small pillows of cartilage that help to cushion the knee bones.

They also checked for fractures of the tibial spine, a fingerling spit of bone that extends from the tibia, or shinbone, to which the A.C.L. attaches. In prepubescent children whose skeletons are still growing, the slender tibial spine can be weaker than the tissues of the A.C.L. and break under the pressures of hard twisting or planting of the knee, even as the A.C.L. remains intact. “There was a time when the tibial spine fracture was the knee injury of childhood,” Dr. Lawrence says. “Twenty years ago, medical textbooks usually included a statement saying that kids did not tear their A.C.L., that they fractured the tibial spine instead.”

But when the researchers examined the pediatric hospital records, from 1999 through early this year, they found only 155 tibial spine fractures, while there were 914 confirmed A.C.L. tears and 996 meniscus tears. More important, while the incidence of tibial spine fractures increased at a rate of about 1 percent per year during that period, the incidence of A.C.L. tears increased by more than 11 percent per year. The difference almost certainly was not a result of better equipment leading to better diagnoses of A.C.L. tears, Dr. Lawrence says. “Even in 1999, M.R.I. technology was quite good,” so it was possible for physicians to differentiate between the injuries.

Which means that increasingly large numbers of young athletes, both boys and girls, are now suffering an injury to which doctors once thought they were almost immune.

Why? Scientists still aren’t sure, and that question was outside the scope of the current analysis. But Dr. Lawrence, a pediatric orthopedic surgeon who treats many of the afflicted young athletes, is willing to speculate. “I think it’s primarily because kids are out there trying to emulate professional athletes,” he says. “You see these very young athletes playing sports at an extremely intense, competitive level. Kids didn’t play at that level 20 years ago. They didn’t play one sport year-round.” As a consequence, their knees never had to withstand the kinds of repeated twists, sprints, loads and hard hits that young players now regularly absorb, he says.

Most of the A.C.L. tears that were treated at Children’s Hospital and picked up by this study, Dr. Lawrence points out, also involved a simultaneous meniscus tear, an indication of just how much wrenching and grinding the knee had undergone. Injury patterns have changed, he continues, because childhood sports have changed. “There’s a developmental soccer team here” in Philadelphia, he says, “for U-6 players,” meaning a competitive, select team for 4- and 5-year-olds. “When I heard that, I said, are you kidding me?”

The long-term effects of sports-related A.C.L. and meniscus tears in youngsters remain largely unknown, in part because such injuries were so rare decades ago. But there are indications that the consequences could be calamitous.

Recent studies of adult Swedish soccer players who tore an A.C.L. found that, within 12 to 14 years after the injury, 51 percent of the female players and 41 percent of the men had developed severe arthritis in the injured knee. The same time frame could have an injured 10-year-old dealing with a severely arthritic knee before he or she is 25. Meanwhile, many athletes who return to sports after an A.C.L. tear report that they don’t play as well, according to a new study of 500 Australian athletes, and a third of the athletes in that study did not return to any activity afterward.

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“It’s definitely not a minor injury,” Dr. Lawrence says, “and it’s not something you want to see in a child.”

Whether anything can be done to lessen the toll on young knees, though, is uncertain, he and other researchers say. Knee injury prevention programs, including those that teach balance and proper landing techniques, have shown some utility in reducing the incidence of A.C.L. tears, especially in girls. But the programs are relatively new and have not been universally successful, in part, perhaps, because they can make some young athletes overly self-conscious, as an interesting review article published earlier this year suggests. In teaching children to think overtly about how to plant a leg or bend a knee while maintaining balance, some youngsters may become less fluid in their movement, more ungainly — and potentially ripe for injury, the review’s authors speculate.

A better solution would probably be to stop assuming that children can train like miniature Ronaldos or Kobe Bryants. “A lot of what we see in our injury data is almost certainly due to a statistical measure called exposure hours,” Dr. Lawrence says. “The more you do a risky activity at a high level, the more likely you are to get hurt.” His advice? “Encourage kids to play multiple sports and not to do any one sport year-round, and especially not when they’re 5 or 6, or even 9 or 10. They’re kids. Let them play and have fun, like kids.”

Tara Parker-Pope

Tara Parker-Pope writes about health for the New York Times. She can be reached via email.

Last modified: October 27, 2011
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